Hamish, This is a really nice page. Thanks for sharing it.
Michael On 10/20/07 9:31 PM, "Hamish" <[EMAIL PROTECTED]> wrote: > Thomas Adams wrote: >> I'm wondering if someone has a color map that has white in the middle >> range and blue at one extreme and red at the other. I'm creating a >> precipitation difference map for data quality control purposes and I'm >> trying to identify areas of over- and under-estimation by radar >> estimates relative to gauge-only estimates. Such a scale would be >> helpful to those looking for differences. > > Glynn wrote: >> The "differences" map (i.e. "r.colors ... color=differences") is: >> 0% blue >> 0 white >> 100% red >> >> This may be suitable, depending upon what you mean by "white in the >> middle". The above has white at zero, which isn't necessarily the >> middle. If you want white at the midpoint between the minimum and >> maximum values, use: >> 0% blue >> 50% white >> 100% red >> >> If you want the table to be symmetrical, you'll need to specify >> absolute values rather than percentages, e.g.: >> -10 blue >> 0 white >> 10 red > > > Doing a symmetrical absolute value color maps interests me, so I wrote a > script to do it automatically based on r.univar results. It's called > r.colors.stddev and it is now u on the wiki addons page. Read all about it & > screenshots here: > http://hamish.bowman.googlepages.com/grass_color_maps > > I am not a statistician, so take my approach with a grain of salt and > improvements are welcome. -- The book "How to lie with statistics" could > easily have a second edition "How to lie with the human eye and color rules". > > > One problem that came up, the r.univar percentile= option only takes integer > values. You can pass it a FP number but it just chops off everything after the > decimal point. (I wanted the percentile values for 68.2689%, 95.4500%, > 99.7300% of area under the curve, right now r.univar casts those to int so > results are not exactly right) I have patched it locally (int->double, > %d->%lf,%g), but it causes a few little problems: > > 1) cosmetic: there are rules for the 1st 2nd 3rd 4-9,0th percentile text. > It would need to be updated to use the least significant digit from %g. > Also that has i18n concerns... > > 2) the percentile shell script output would get a "." in it, which is invalid > for an environment variable $name. It could be replaced with an underscore, > ....? > > 3) It gives an answer, but is it an appropriate/meaningful thing to calculate? > (tiny doubt lingers) > > > enjoy, > Hamish > > __________________________________________ Michael Barton, Professor of Anthropology Director of Graduate Studies School of Human Evolution & Social Change Center for Social Dynamics & Complexity Arizona State University phone: 480-965-6213 fax: 480-965-7671 www: http://www.public.asu.edu/~cmbarton _______________________________________________ grassuser mailing list grassuser@grass.itc.it http://grass.itc.it/mailman/listinfo/grassuser